Last year my potted impatiens had that terrible new disease, impatiens downy mildew, and all died. Can I use my old infected potting soil in non-flower beds this year? Send it to the landfill?

Impatiens downy mildew spores overwinter in infected plant debris, not soil per se. Remove all obvious plant debris and a couple of the top inches of soil that may have minute bits of debris in it. Send that to the landfill. You can use the rest of the potting soil elsewhere in your landscape, but do be careful to wash and disinfect your pots before reusing them.

My neighbor said I can use salt to control weeds in an asparagus bed. Seems like it would kill it?

Asparagus will grow happily in brackish water and will tolerate being flooded with salt water once a year. (The salt has some ability to ward off crown and root rot diseases in declining beds.) Applying salt for weed control kills only young, germinating weed seeds, not mature weeds. It is far better to simply bite the bullet — do a thorough weeding — then mulch well. At the end of the season, apply more mulch, but be sure to pull it back for the emerging spears next spring.

University of Maryland Extension's Home and Garden Information Center offers free gardening and pest information. Call 800-342-2507 or send a question to the website at extension.umd.edu/hgic.

Plant of the Week

Heliopsis, false sunflower

Heliopsis helianthoides

Heliopsis bears bright yellow daisy-like flowers in glorious profusion from early summer through early autumn. This under-utilized native perennial, also known as oxeye sunflower, is a bushy plant, useful in a sunny summer flower border or wildflower meadow. They are magnets to pollinators, butterflies and even hummingbirds and combine beautifully with other summer perennials, such as garden phlox. Plant them in moist or dry, average to rich soil in full to part sun, though they bloom best with full sun. Many cultivars are now available, making them easier than ever to use in an array of garden situations. — Christine McComas